1. Field of the Invention
The present invention relates, in general, to a method for fabricating a phase shift mask, and more particularly, to a method for improving the production cost and yield of the phase shift mask.
2. Description of the Prior Art
A typical photolithography process for a semiconductor device employs a mask comprising a transparent substrate, such as quartz, on which light screen patterns of chrome are formed. However, it is virtually impossible to form photosensitive patterns with a good profile by using the typical chrome mask, in a lesser dimension than can be formed by current light exposing equipments because interference is caused at the narrow distance between the chrome patterns. Indeed, the typical chrome mask is not applied in the fabrication of a semiconductor device of 64M or more.
Various efforts have been made to overcome this problem. In an effort to develop highly integrated semiconductor devices, a phase shift mask comprising a quartz substrate was developed on which a plurality of spaced chrome patterns are formed with a phase shift pattern between the two chrome patterns.
In such phase shift mask, the light passing through the quartz substrate has a phase shifted at an angle of 180.degree. to the light passing through the phase shift patterns. Therefore, the intensity of light shows zero at the interface between the quartz substrate and the phase shift patterns, thereby improving the profile of photosensitive film patterns.
The use of such a phase shift mask in a photolithography process makes the process capability better by 50% or more than the use of conventional chrome masks. In addition, the phase shift mask is capable of forming photosensitive film patterns which are finer than the limit of the light exposing equipments used.
However, the phase shift mask is difficult to design and fabricate, demanding additional equipments. Also, the fabrication of the phase shift mask by prior art methods requires high costs and much time.